In the so-called Marshall construction, each coil spring is encased within its own fabric sack, which is generally made in the form of a pocket defined between two plies of a fabric strip connected together at intervals along transverse lines spaced along the strip. The two-ply strip is generally formed by folding a strip of fabric upon itself along its longitudinal centerline, leaving the overlapped plies along the unjoined opposite edges of the strip to be connected to each other to close the pockets defined between the transverse lines of connection after the springs are inserted.
In accordance with one known method and apparatus for inserting and compressing coil springs between opposed plies of a fabric strip and thereafter securing the plies transversely and longitudinally to form closed pockets, the plies of fabric are secured by thread stitching. The mechanical requirements upon sewing machines for accomplishing the requisite stitching in making series connected individually pocketed springs are severe, and the mechanisms required for moving the sewing machines in relation to the fabric strip, particularly in accomplishing the transverse stitching which defines the pockets, has of necessity been complicated. The productivity of such machines is generally limited by the limitations of the sewing machines, including the problem of thread breakage.
Therefore, a method of ultrasonically welding a ply of fabric together was developed, disclosed in U.S. Pat. Nos. 4,234,983 and 4,439,977, both of which are incorporated by reference.
As seen in U.S. Pat. No. 4,439,977, various pneumatic cylinders are used to provide various operations, such as the driving of ultrasonic heads and insertion of compressed coils. Furthermore, a folding assembly is shown which utilizes a fabric folder indicated generally as 24. A length of pocketed coils, now referred to as a pocketed coil string, are provided such that shown in U.S. Pat. No. 4,234,983. Such pocketed coil strings may be fastened by adhesives in order to provide innerspring constructions such as that shown in U.S. Pat. No. 4,578,834, herein incorporated by reference.
In reference to U.S. Pat. No. 4,234,983, transverse lines of attachment 10 combined with longitudinal lines of attachment 18 in order to provide pockets for the coil springs therein. It may be appreciated that it is preferable that the free edges of the folded fabric 24 should preferably be in coalignment. It should also be appreciated that a certain distance must be had between the longitudinal line connection of 18 and the fabric edges 24, in order to provide sufficient strengths to the line 18 of connection and discourage separation thereon.
The above methods, apparatuses, and configurations includes several advantages, although shortcomings do exist. For example, it may be understood that a need exists for a method and apparatus for manufacturing pocketed coil strings which provides accurate coalignment of the free edges of the fabric, in order to discourage fabric waste. Furthermore, a need exists for accurate positioning of the folded fabric when passing underneath the weld heads, particularly the longitudinal weld head, in order that a longitudinal weld line is accurately positioned an acceptable distance from the free edges of the fabric. If the weld is too far from the free edges, fabric is wasted. If the longitudinal weld line is too close to the free edges of the fabric, the weld line may be weak and prone to separation.
Furthermore, a need has arisen for a more "gentle" feed of the fabric from the feed roll and through the folding process. In the prior art apparatuses, the fabric is "indexed" one pocket width distance in each cycle, with this indexing being done in a single step followed by a dwell step. For high speeds and/or large pocket widths, this feed technique can result in excessive stresses on the fabric downstream of the weld station, which may result in unacceptable folding, tracking, or feeding. Therefore, a need exists for an improved feed system.
Additionally, a need has arisen to eliminate, to as much extent as possible, pneumatic cylinders used to drive and/or operate various elements of an apparatus for manufacturing pocketed coil strings. It has been found that, especially in colder regions, pneumatic air cylinders tend to require an extensive warm up period. Furthermore, such air cylinders tend to require a great deal of adjustment if the machine is to be operated during the warm up period. Finally, it has been found that the very nature of pneumatic cylinders requires that they be repeatedly adjusted throughout their lifetimes. Finally, air cylinders tend to limit the maximum operating speed of a particular apparatus. In light of these disadvantages, a need has arisen to eliminate as many pneumatically-controlled processes as possible in order to reap the advantages in both speed and maintenance of direct-drive configurations.
These and other needs prompted the development of the apparatus 10, in particular, certain of its elements, illustrated in the following description.